1. Field of the Invention
The present invention generally relates to a combustion chamber structure for an internal combustion engine. More specifically, the present invention relates to a combustion chamber structure for an internal combustion engine in which an air-fuel mixture is drawn into a combustion chamber and combusted in the combustion chamber.
2. Background Information
A combustion chamber for an internal combustion engine with a piston reciprocating therein is usually formed by a lower surface of a cylinder head, a piston crown surface, and a cylinder bore wall surface. The lower surface of the cylinder head includes a plurality of intake openings and a plurality of exhaust openings. With an internal combustion engine in which a fuel injector is provided along an intake passage that opens to the combustion chamber through the intake openings, an air fuel mixture flows into the combustion chamber when intake valves coupled to the intake openings are opened. Then, after the fuel is combusted in the combustion chamber, the burned exhaust gas is discharged to an exhaust port by opening the exhaust openings by controlling the exhaust valves coupled to the exhaust openings.
For example, Japanese Laid-Open Patent Application H7-150945 discloses a combustion chamber structure in which a step structure is provided in a lower surface of the cylinder head around each intake opening. More specifically, in this reference, intake opening peripheral wall surfaces that surround the intake openings are provided to form a stepped surface around each intake opening. With such a combustion chamber structure, when the internal combustion engine has a variable lift mechanism configured and arranged to variably control an amount of valve lift, even when an amount of intake valve lift is reduced so that the amount of air-fuel mixture drawn into the combustion chamber is throttled, the air-fuel mixture that flows into the combustion chamber hits the stepped surfaces formed around the intake openings and changes the direction of the air-fuel mixture to move away from the cylinder head lower surface. As a result, the combustion state of the internal combustion engine is stabilized even when the valve lift amount of the intake valves is reduced when the internal combustion engine is operating in low engine speed or under low load operating condition.
Moreover, in the above mentioned reference, the stepped surface is formed such that when the intake valve is opened the gap between the stepped surface and the outer periphery surface of the intake valve is wider on the side close to the spark plug and narrower on a side opposite from the spark plug. With such a structure, tumble and swirl flow within the combustion chamber is increased as disclosed in the above mentioned reference.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved combustion chamber structure for internal combustion engine. This invention addresses this need as well as other needs, which will become apparent to those skilled in the art from this disclosure.